The invention relates to a sub-assembly for detecting leaks of a liquid metal circulating in a component of a circuit such as a conduit or a valve or contained in a storage means such as a reservoir, and a detection apparatus comprising a plurality of sub-assemblies of this type.
In certain applications, notably in breeder nuclear reactors, a liquid metal such as molten sodium circulates in the circuits. For obvious safety reasons, particularly when the liquid metal is sodium, it is necessary to be able to detect leaks of this metal, along the circuit or in a reservoir containing the metal, rapidly and accurately.
A certain number of apparatus have been proposed for detecting leaks of this kind. The majority of these apparatus comprise electrically conductive elements, in the form of wires, plates or grids, for example, associated with an electrically insulating support material interposed between these electrically conductive elements and the conduit in which the liquid metal circulates. The support consisting of insulating material may consist, for example, of woven silica threads or a layer of permeable felt. Depending on the particular apparatus, a leak of the liquid metal is detected either by the establishing of electrical contact between two adjacent electrically conductive elements or by the establishing of an electrical contact between one or more of these electrically conductive elements and the conduit. In every case, the leak is not detected until the liquid metal leaking out has passed through the support of electrically insulating material, which does not usually occur until after a relatively long time, up to several minutes. Obviously, this response time is not adequate, particularly when the liquid metal is sodium, owing to the risk of fire created by the existence of a leak. Moreover, the known apparatus are fragile and have to be handled with great care, particularly when they operate at relatively high temperature, as is the case when they surround conduits in which liquid sodium is circulating.